Label made of polyolefin film

ABSTRACT

The invention relates to the use of a multi-layer polypropylene film as an in-mold label used in a blow molding methods. According to the invention, the label film is laid inside the hollow mold of a blow molding machine, comprises an inner protective layer that faces the receptacle to be molded, and comprises an outer protective layer that is in contact with the hollow mold, whereby the inner protective layer has a roughness Rz of at least 3.5  mu m.

The present invention relates to the use of a polypropylene film asin-mold label for blow molding.

In the blow molding of hollow articles, a tube of a suitable polymer isextruded continuously or batchwise. The tube is laid in a multipart moldcavity, pinched off at the lower end and at the same time cut off at theupper end. A nozzle is inserted in a tightly fitting manner into theupper opening which remains, and air is blown in through this nozzleduring the actual blowing operation. In the process, the tube bubble isblown up and brought into close contact with the wall of the mold. Themold is then opened, tubes projecting at the top and bottom are removedfrom the demolded blow molding, and the process is started afresh.

Labeling during production of containers by blow molding is known in theprior art and is referred to as in-mold labeling. In this process, alabel is laid in the opened blow mold, usually by a robot, in such a waythat the printed outside of the label is in contact with the mold wall,and the unprinted inside faces the blow molding to be shaped. Duringintroduction of the tubular melt and shaping of the blow molding by theair pressure, the still-plastic surface of the polymer composition comesinto close contact with the label and bonds thereto to give a labeledcontainer.

In this labeling process, it must be ensured that the label lies againstthe mold wall in a flat and fold-free manner. This is achieved either bymeans of vacuum applied to fine air-removal perforations in such a waythat the perforations are substantially sealed by the label, or by meansof electrostatic forces between the electrostatically charged label andthe earthed mold.

In this production process, the label is either, particularly in thecase of simple label shapes, supplied in roll form and cut to size atthe blow-molding machine (“cut in place”) or, in the case of morecomplex label shapes, cut to size in advance and away from theblow-molding machine, stacked and later segregated from the stack at theblow-molding machine (cut & stack process) and introduced individuallyinto the respective blow mold.

Films made from thermoplastics have recently increasingly been used forthe labeling of containers. The films which are suitable for a use ofthis type have to have a selected property profile in order to ensurethat the label film and molding nestle against one another in a flat andbubble-free manner and bond to one another. Solutions, in some casestechnically complex, have been found for this in the prior art. Thus, inone embodiment, a BOPP film is coated on the inside with an adhesive ina cross-hatch pattern. It is known that a coating of this type isassociated with considerable costs.

In addition, the various printing processes and labeling processesrequire different film properties, in particular different propertyprofiles. This means that very frequently it is not just a single goodproperty that facilitates use of the film for the proposed purpose.Instead, only a large number of properties which have to be achievedsimultaneously in a film guarantee usability for the proposed purpose.

Thus, the use of an opaque film has been proposed for blow-mold in-moldlabeling, which film has at least one base layer comprisingvacuole-initiating fillers and pigments, and top layers on both sides ofthis base layer, where the film has a total thickness of at least 85 μm,and the base layer comprises a combination of tertiary aliphatic amineand fatty acid amide and the two top layers comprise antiblockingagents, and the density of the film is in a range from 0.65 to 0.85g/cm³ and has been corona- or flame-treated on both sides.

It has furthermore been proposed to employ opaque films of this type incombination with special additive formulations and specially selectedfilm thicknesses in order to guarantee the usability thereof for thepurpose according to the invention.

The known films are suitable in accordance with the invention forlabeling blow moldings having a flattened oval cross section, inparticular on the flatly curved surfaces. In the case of blow moldingshaving smaller radii of curvature, for example having a round-oval crosssection or in the case of labeling of the narrow sides of flattened ovalblow moldings, bubbles occur which have a considerable adverse effect onthe appearance. These bubbles are generally tightly filled with air.

The object of the present invention was to provide an inexpensive labelfilm which is intended to be suitable for in-mold labeling in theblow-molding process. In particular, it should be possible to apply thefilm as bubble-free label to curved bodies, including those having asmall radius of curvature, and should not have any other opticaldefects. At the same time, other important service properties of thefilm, such as gloss, printability and destackability, must not beimpaired.

The object on which the invention is based is achieved by the use of amultilayered polypropylene film as an in-mold label in the blow-moldingprocess. In the use according to the invention, the label film isinserted into the mold of a blow-molding machine. The label film has aninner top layer facing the container to be molded and an outer top layerwhich is in contact with the mold. The inner top layer has a roughnessRz of at least 3.5 μm.

It has been found that the rough inside of the label film guarantees itsusability for the purpose according to the invention.

In a preferred embodiment, the film used as blow-mold label is an opaquefilm. For the purposes of the present invention, the term “opaque film”means a non-transparent film whose transparency to light (ASTM-D1003-77) is at most 70%, preferably at most 50%.

The base layer of the multilayered film generally comprises apolyolefin, preferably a propylene polymer, and optionallyvacuole-initiating fillers and further additives in effective amounts ineach case. In general, the base layer comprises at least 50% by weight,preferably from 60 to <100% by weight, in particular from 70 to <100% byweight, of the polyolefin, in each case based on the weight of thelayer.

Preferred polyolefins are propylene polymers. These propylene polymerscomprise from 90 to 100% by weight, preferably from 95 to 100% byweight, in particular from 98 to 100% by weight, of propylene units,have a melting point of 120° C. or above, preferably from 150 to 170°C., and generally have a melt flow index of from 0.5 to 8 g/10 min,preferably from 2 to 5 g/min, at 230° C. and a force of 2.16 kg (DIN53735). Isotactic propylene homopolymer having an atactic content of 15%by weight or less, copolymers of ethylene and propylene having anethylene content of 5% by weight or less, copolymers of propylene withC₄-C₈-olefins having an olefin content of 5% by weight or less,terpolymers of propylene, ethylene and butylene having an ethylenecontent of 10% by weight or less and having a butylene content of 15% byweight or less are preferred propylene polymers for the base layer, withisotactic propylene homopolymer being particularly preferred. The statedpercentages by weight are based on the respective polymer.

Also suitable is a mixture of said propylene homopolymers and/orcopolymers and/or terpolymers with other polyolefins, in particular madefrom monomers having from 2 to 6 carbon atoms, where the mixturecomprises at least 50% by weight, in particular at least 75% by weight,of propylene polymer.

Suitable other polyolefins in the polymer mixture are polyethylenes, inparticular HDPE, LDPE, VLDPE and LLDPE, where the proportion of thesepolyolefins is in each case not in excess of 15% by weight, based on thepolymer mixture.

In the opaque embodiment, the opaque base layer of the film comprisesfillers in a maximum amount of 40% by weight, preferably from 1 to 30%by weight, in particular from 2 to 20% by weight, based on the weight ofthe opaque layer. For the purposes of the present invention, the fillersare pigments and/or vacuole-initiating particles.

For the purposes of the present invention, pigments are incompatibleparticles which essentially do not result in vacuole formation when thefilm is stretched. The coloring action of the pigments is caused by theparticles themselves. In general, the mean particle diameter of thepigments is in the range from 0.01 to 1 μm, preferably from 0.01 to 0.7□m, in particular from 0.01 to 0.4 □m. Conventional pigments arematerials such as, for example, aluminum oxide, aluminum sulfate, bariumsulfate, calcium carbonate, magnesium carbonate, silicates, such asaluminum silicate (kaolin day) and magnesium silicate (talc), silicondioxide and titanium dioxide, of which preference is given to the use ofwhite pigments, such as calcium carbonate, silicon dioxide, titaniumdioxide and barium sulfate.

The titanium dioxide particles generally comprise at least 95% by weightof rutile and are preferably employed with a coating of inorganic oxidesand/or of organic compounds containing polar and nonpolar groups. TiO₂coatings of this type are known in the prior art.

For the purposes of the present invention, “vacuole-initiating fillers”are solid particles which are incompatible with the polymer matrix andresult in the formation of vacuole-like cavities when the films arestretched, with the size, nature and number of the vacuoles beingdependent on the size of the solid particles and the stretchingconditions, such as stretching ratio and stretching temperature. Thevacuoles reduce the density and give the films a characteristicpearl-like opaque appearance caused by light scattering at the“vacuole/polymer matrix” interfaces. In general, the mean particlediameter of the particles is from 1 to 6 μm, preferably from 1.5 to 5μm. The chemical character of the particles plays a secondary role.

Conventional vacuole-initiating fillers are inorganic and/or organic,polypropylene-incompatible materials, such as aluminum oxide, aluminumsulfate, barium sulfate, calcium carbonate, magnesium carbonate,silicates, such as aluminum silicate (kaolin clay) and magnesiumsilicate (talc), and silicon dioxide, of which calcium carbonate andsilicon dioxide are preferred. Suitable organic fillers are theconventional polymers which are incompatible with the polymer of thebase layer, in particular those such as HDPE, copolymers of cyclicolefins, polyesters, polystyrenes, polyamides and halogenated organicpolymers, preference being given to polyesters, such as, for example,polybutylene terephthalate, and cycloolefin copolymers. For the purposesof the present invention, “incompatible materials or incompatiblepolymers” means that the material or polymer is in the film in the formof a separate particle or separate phase.

The base layer optionally comprises pigments in an amount of from 0.5 to10% by weight, preferably from 1 to 8% by weight, in particular from 1to 5% by weight. Vacuole-initiating fillers are preferably present in anamount of from 0.5 to 25% by weight, preferably from 1 to 15% by weight,in particular from 1 to 10% by weight. The data are based on the weightof the base layer.

The vacuole-initiating fillers reduce the density of the film. It hasbeen found that, in a preferred embodiment, it is particularlyadvantageous to keep the density of the film within narrow limits,preferably in a range from 0.5 to 0.85 g/cm³, in particular between 0.65and 0.85. Films having a density of less than 0.5 are difficult toproduce and, on use as in-mold labels in blow molding, frequentlyexhibit optical defects in the form of the so-called orange-peel effect,where the label film is deformed on the surface with formation ofmillimeter-sized bubbles. If the density is greater than 0.85 g/cm³, theadhesion to the container becomes worse.

Besides the preferably opaque base layer, the film according to theinvention comprises an inner and an outer top layer. For the purposes ofthe present invention, top layers are outer layers whose outer surfaceforms the film surface. For the purposes of the present invention, theinner surface, or the inner top layer, is that side of the film whichfaces the container and bonds to the molding during blow molding. Theouter surface or top layer is naturally the opposite side, which is incontact with the blow mold during the labeling process and forms theouter surface in the labeled container.

The outer top layer of the multilayered film generally comprises atleast 70% by weight, preferably from 75 to <100% by weight, inparticular from 90 to 98% by weight, of a propylene polymer and ingeneral antiblocking agents and stabilizers and, if desired, furtherconventional additives, such as lubricants, for example fatty acidamides or siloxanes, in effective amounts in each case. Preference isgiven to embodiments of the outer top layer which comprise fatty acidamides. The above data in % by weight are based on the weight of the toplayer.

The propylene polymer of the outer top layer is preferably a copolymerof propylene and ethylene or propylene and butylene or propylene andanother olefin having from 5 to 10 carbon atoms. Also suitable for thepurposes of the invention are terpolymers of ethylene and propylene andbutylene or ethylene and propylene and another olefin having from 5 to10 carbon atoms. It is also possible to employ mixtures or blends of twoor more of said copolymers and terpolymers.

For the outer top layer, preference is given to ethylene-propylenecopolymers and ethylene-propylenebutylene terpolymers, in particularrandom ethylene-propylene copolymers having an ethylene content of from2 to 10% by weight, preferably from 5 to 8% by weight, or randomethylene-propylene-1-butylene terpolymers having an ethylene content offrom 1 to 10% by weight, preferably from 2 to 6% by weight, and a1-butylene content of from 3 to 20% by weight, preferably from 8 to 10%by weight, in each case based on the weight of the copolymer orterpolymer.

The copolymers and terpolymers described above generally have a meltflow index of from 1.5 to 30 9/10 min, preferably from 3 to 15 g/10 min.The melting point is in the range from 120 to 140° C. The blend ofcopolymers and terpolymers described above have a melt flow index offrom 5 to 9 g/10 min and a melting point of from 120 to 150° C. All themelt flow indices given above are measured at 230° C. and a force of2.16 kg (DIN 53735).

In accordance with the invention, the inner surface of the multilayeredfilm is rough. The Rz value (at a cut-off value of 0.25 mm) of theroughness here is at least 3.5 μm, preferably from at least 4.0 to 10μm, in particular from 4.5 to 8 μm. It has been found that a rough innersurface of the film has a very favorable effect on its use as blow-moldlabel. Against expectations, the adhesion to the container is at thesame time not impaired by the rough surface. It has been found that, inparticular, the formation of bubbles is greatly reduced, and in somecases even completely prevented, even in the case of relatively highlycurved surfaces.

The surface roughness presumably contributes toward air cushions whichform between the container and label during blow molding not beingincluded. The rough surface forms fine channels which facilitate escapeof the air.

In principle, various ways of producing a rough surface are available tothe person skilled in the art. As part of the present invention, it hasbeen found that it is particularly advantageous to produce thisroughness by blending polypropylene with incompatible or partiallycompatible polymers. This process is technically simple to implementsince the production of rough surfaces by mixing incompatible polymersis known per se in the prior art. It has been found that, in this way,sufficient roughness is formed in order to facilitate “deaeration” ofthe applied label, but at the same time the adhesion to the molding isnot impaired. In addition, other important processing properties of thefilm are not adversely affected or are even favorably affected, forexample the film can be destacked better.

The inner top layer of the multilayered film therefore preferablyconsists of a mixture or blend of two incompatible or only partiallycompatible plastics which separate from one another in separate phasesduring production of the film. A suitable mixture can essentiallyconsist, for example, of polyethylenes PE and polypropylenes PP.Mixtures which essentially consist of PE and propylene copolymers orterpolymers have proven particularly suitable here. The mixing ratiohere is selected in such a way that the inner surface of themultilayered film has a suitable roughness. Mixtures of PE and PP orpropylene copolymers and terpolymers are suitable for the application ifthe mixing ratio (weight ratio) is between PE:PP=1:12 and 5:1, inparticular between 1:5 and 1:1.6.

The polyethylene of the mixture described above can be a high-density orlow-density polyethylene, it being possible to prepare the latter eitherby the high-pressure or the low-pressure (or Ziegler-Natta) process. Themelt flow index, measured at 190° C./2.16 kg, here can be between 0.1and 30 g/10 min, preferably between 0.1 and 10 g/10 min in particularfrom 0.5 to 5 g/10 min.

The propylene polymer of the mixture for the inner top layer ispreferably a copolymer of propylene and ethylene or propylene andbutylene or ethylene and butylene or propylene and another olefin havingfrom 5 to 10 carbon atoms. Also suitable for the purposes of theinvention are terpolymers of ethylene and propylene and butylene orethylene and propylene and another olefin having from 5 to 10 carbonatoms. It is also possible to employ mixtures or blends of two or moreof the said copolymers and terpolymers.

For the mixture with PE, preference is given to ethylene-propylenecopolymers and ethylene propylene-butylene terpolymers, in particularrandom ethylene-propylene copolymers having an ethylene content of from2 to 10% by weight, preferably from 5 to 8% by weight, or randomethylene-propylene-1-butylene terpolymers having an ethylene content offrom 1 to 10% by weight, preferably from 2 to 6% by weight, and a1-butylene content of from 3 to 20% by weight, preferably from 8 to 10%by weight, in each case based on the weight of the copolymer orterpolymer.

The copolymers and terpolymers described above generally have a meltflow index of from 1.5 to 30 g/10 min, preferably from 3 to 15 g/10 min.The melting point is in the range from 120 to 140° C. The blend ofcopolymers and terpolymers described above has a melt flow index of from5 to 9 g/10 min and a melting point of from 110 to 150° C. All the meltflow indices given above are measured at 230° C. and a force of 2.16 kg(DIN 53735).

The inner top layer generally comprises at least 70% by weight,preferably from 75 to <100% by weight, in particular from 90 to 98% byweight (based on the weight of the top layer), of the mixture ofpropylene polymers and polyethylene. In addition, antiblocking agentsand stabilizers and, if desired, further conventional additives, such aslubricants, for example fatty acid amides or siloxanes, may be presentin effective amounts in each case.

For the purposes of the present invention, it is likewise possible toproduce a suitable surface roughness of the inner top layer by othermeasures. For example, it is possible to increase the formation ofβ-spherolites on cooling of the pre-film by technical measuresassociated with the process or by corresponding , β-nucleating agents inthe inner top layer, with pit-like deformations being formed on thesurface during subsequent stretching which likewise facilitatedeaeration of the label during labeling. Mechanical methods, such as,for example, embossing methods, are basically also possible, albeit notpreferred, since downstream measures of this type are expensive.

With respect to the additives present, it is preferred for the baselayer to comprise a tertiary aliphatic amine in an amount of from 0.02to 0.3% by weight, preferably from 0.05 to 0.2% by weight, and fattyacid amides in an amount of from 0.04 to 0.4% by weight, preferably from0.07 to 0.25% by weight, and glycerol monostearate in an amount of from0.05 to 0.4% by weight, preferably from 0.10 to 0.25% by weight.

Tertiary aliphatic amines include compounds of the general formula R₃N,in which R is a fatty acid radical or a C₁₂-C₁₈-alkyl radical or ahydroxyl-substituted alkyl radical, where the radicals R may beidentical or different. Hydroxyl-substituted alkyl radicals arepreferably hydroxyethyl, hydroxypropyl or hydroxybutyl radicals.Particular preference is given to N,N-bis(2-hydroxyethyl)alkylamines. Inindustry, use is frequently made of mixtures of differently substitutedtertiary aliphatic amines, which may also contain hydroxyalkyl chainsextended by oxyalkylidene groups. In addition, N,N-bishydroxyalkyl fattyacid esters may also be used.

The carboxamides include amides of a carboxylic acid having from 8 to 24carbon atoms, or mixtures of these amides. Particular preference isgiven to erucamide, oleamide, stearamide and the like.

Suitable glycerol monostearates are in industry likewise substancemixtures which, besides the stearyl radical, may also contain furtherfatty acid radicals and differ with respect to the substitution patternon the glycerol radical. Particularly advantageous mixtures are thosehaving a high proportion of alpha-glycerol monostearate.

The usual amount of antiblocking agent in the top layers is in the rangefrom 0.05 to 2% by weight, preferably from 0.15 to 0.6% by weight. Fattyacid amides may be present in the top layer in an amount of from 0.05 to0.3% by weight. In addition, the top layers may also comprise siloxanesin an amount of from 0.05 to 1.0% by weight, preferably from 0.1 to 0.5%by weight.

Suitable antiblocking agents are inorganic additives, such as silicondioxide, calcium carbonate, magnesium silicate, aluminum silicate,calcium phosphate and the like, and/or incompatible organic polymers,such as polyamides, polyesters, polycarbonates, and/or crosslinkedorganic polymers, such as polymethacrylates and polysiloxanes and thelike, preference being given to benzoguanamine-formaldehyde polymers,silicon dioxide and calcium carbonate. The mean particle size is between1 and 6 μm, in particular between 2 and 5 μm.

The total thickness of the film is generally at least from 50 to 150 □m,preferably from 60 to 120 □m, in particular from 75 to 100 □m. Thinfilms of less than 50 □m, in spite of a rough inside surface, readilyexhibit bubbles on use as a label, which frequently appear full tobursting or inflated.

The thickness of the outer top layer is preferably in the range from 0.3to 5 μm, in particular from 0.7 to 2.5 μm. Within the scope of thepresent invention, it has been found that a comparatively thick outertop layer is advantageous for the film appearance, which is advantageousfor the quality of the print image on the printed outside of the labelfilm. It has been found that, for opaque base layers having a layerthickness of up to 70 μm, the top layer thickness is comparativelyunimportant. It has been found that a uniform appearance is particularlydifficult to achieve with very thick opaque base layers of greater than80 μm. This problem has been solved by providing the thick opaque baselayer with particularly thick top layers of greater than 1.5 μm.

The layer thickness of the inner top layer is generally in a range from0.5 to 5 μm. Advantages with respect to adhesion of the label to theblow molding arise if the layer thickness of the inner top layer is inthe range from 1 to 4 μm, preferably from 2 to 4 μm. Furthermore,particularly good flat lying arose on processing of the film (printing,stacking and segregation) if the thickness of the top layer on theinside was equal to or not greater than 100% higher than the top layeron the inside.

In order very substantially to meet the various requirements, anembodiment of the film having an outer top layer of from 1.5 to 2.5 μmand an inner top layer of from 2.5 to 4 μm is particularly advantageous.

The film according to the invention has at least three layers and alwayscomprises as essential coextruded layers the base layer and at least onetop layer on both sides, with embodiments having an opaque base layerbeing preferred. If desired, four- and five-layered embodiments are alsopossible, in which the opaque layer forms the base layer of the film andan interlayer has been applied to the surfaces of the base layer on oneor both sides.

Frequently encountered embodiments of BOPP films are corona- orflame-treated on one side, preferably on the outer top layer, in orderto anchor printing inks, metal layers or adhesives to be applied.

The opposite, inner side usually remains untreated. On laying in theblow-molding machine in accordance with the cut & stack process, thein-mold label film according to the invention proved to be particularlysimple and reliable to segregate in an embodiment with corona- orflame-pretreatment on both sides.

The invention furthermore relates to a process for the production of themultilayered film according to the invention by the coextrusion process,which is known per se.

This process is carried out by coextruding the melts corresponding tothe individual layers of the film through a flat-film die, taking offthe resultant film over one or more rolls for solidification,subsequently, if desired, biaxially stretching (orienting) the film,heat-setting the optionally biaxially stretched film, and corona- orflame-treating the film on one side, preferably on both surface layers.

The biaxial stretching (orientation) can be carried out simultaneouslyor consecutively, with consecutive biaxial stretching, in whichstretching is firstly carried out longitudinally (in the machinedirection) and then transversely (perpendicular to the machinedirection), being particularly favorable.

As is conventional in the coextrusion process, the polymer or polymermixture of the individual layers is firstly compressed and liquefied inan extruder, it being possible for any additives added already to bepresent in the polymer. The melts are then forced simultaneously througha flat-film die (slot die), and the extruded multilayered film is takenoff on one or more take-off rolls at a temperature of from 10 to 90° C.,preferably from 20 to 60° C., during which it cools and solidifies.

The film obtained in this way is preferably then stretched in thelongitudinal direction at a temperature of below 140° C., preferably inthe range from 110 to 125° C., in a ratio of from 4:1 to 7:1 and in thetransverse direction at a temperature above 140° C., preferably from 145to 160° C., by a factor of from 6:1 to 11:1. The longitudinal stretchingis advantageously carried out with the aid of two rolls running atdifferent speeds corresponding to the desired stretching ratio, and thetransverse stretching is advantageously carried out with the aid of anappropriate tenter frame.

The biaxial stretching of the film is followed by heat-setting (heattreatment) thereof, in which the film is held at a temperature from 110to 150° C. for from about 0.5 to 10 seconds. The film is subsequentlywound up in a conventional manner by means of a wind-up unit.

After the biaxial stretching, one, preferably both, surface(s) of thefilm is (are), as mentioned above, preferably usually corona- orflame-treated by one of the known methods.

For the alternative corona treatment, the film is passed between twoconductor elements serving as electrodes, with such a high voltage,usually an alternating voltage (about 10,000 V and 10,000 Hz), beingapplied between the electrodes that spray or corona discharges canoccur. Due to the spray or corona discharge, the air above the filmsurface is ionized and reacts with the molecules of the film surface,causing formation of polar inclusions in the essentially non-polarpolymer matrix. The treatment intensities are in the usual range,preferably from 38 to 45 mN/m.

The invention is now explained by the examples below.

EXAMPLE 1

A three-layer film having an ABC layer structure, i.e. a top layer A hadbeen applied to the base layer B on the side intended for printing,referred to as “outer”, and a top layer C had been applied to theopposite, “inner” side, was extruded as the sum by the coextrusionmethod from a flat-film die at an extrusion temperature of 260° C. Thetop layers A and C were corona-treated.

The essential components of the base layer B were the following:

88.65% by weight of a propylene homopolymer (PP) having ann-heptane-soluble content of 4.5% by weight (based on 100% PP) and amelting point of 165° C. and a met flow index of 3.2 g/10 min at 230° C.and a load of 2.16 kg (DIN 53 735);  6.00% by weight of TiO₂ viamasterbatch  ®P 8555 LM, supplier Schulman GmbH, HüttenstraBe 211,D-54578 Kerpen;  0.10% by weight of N,N bis(2-hydroxyethyl)(C₁₀-C₂₀)alkylamine (® Armostat 300)  0.25% by weight of erucamide  5.00% byweight of calcium carbonate having a mean particle size of 3 μm

The top layer A consisted of a random ethylene-propylene copolymer fromSolvay (Eltex PKS 409), having an ethylene content of 4.5% by weight.The melting point of the ethylene-propylene copolymer was 134° C., andthe melt flow index (230° C./2.16 kg) was 7.0 g/10 min.

The top layer C consisted of a mixture of

74.8% by weight of a random ethylene-propylene copolymer from Solvay(Eltex PKS 409), having an ethylene content of 4.5% by weight, a meltingpoint of 134° C. and a melt flow index of 7.0 g/10 min at 230° C. and2.16 kg   25% by weight of an HDPE in blown-film quality having adensity of 0.934 and an MFI of 0.15 g/ 10 min at 190° C. and 2.16 kg, 0.1% by weight of antiblocking agent (® Syloblock 45) and  0.1% byweight of erucamide.

All layers contained 0.12% by weight of pentaerythrityltetrakis[4-(3,5-di-tertiarybutyl4-hydroxyphenyl)propionate] (®Irganox1010) as stabilizer and 0.06% by weight of calcium stearate asneutralizer.

After coextrusion, the extruded three-layer film was, via thecorresponding process steps, taken off and cooled via a first take-offroll and a further trio of rolls, subsequently stretched longitudinally,stretched transversely, set and corona-treated, with the followingconditions, in detail, being selected:

Extrusion: extrusion temperature 260° C. Longitudinal stretching:stretching roll T = 122° C. Longitudinal stretching by a factor of 4.9Transverse stretching: heating zones T = 170° C. Stretching zones T =159° C. Transverse stretching by a factor of 9.5 Setting: temperature T= 115° C. Corona treatment: voltage: 10,000 V frequency: 10,000 Hz

Directly after production, the multilayered film produced in this wayhad a surface tension of from 40 to 41 mN/m on the outer side and from39 to 40 mN/m on the inner side. The film had a thickness ofapproximately 90 μm, with the thickness of top layer A being about 2 μmand that of top layer C being 4 □m. The film had a density of 0.72g/cm³.

The film was printed, cut into the label shape and stacked. The labelstacks were provided in the usual manner at the blow-molding machine. Ablow-molding machine with automatic label feed was fitted with a mold“A” for a bulge-shaped bottle with vertical, upward-facing lip. Thegeometry of the bottle mold A was selected in such a way that ahorizontal section at half the height of the area to be labeled had alength to width ratio of 131 to 91 mm. The blow-molding machine wasloaded with HD-PE blow-molding material and operated under the usualprocessing conditions for HD-PE.

The results of the experiment are described in the table below.

EXAMPLE 2

Example 1 was repeated, with the base layer containing, as lubricant andantistatic,

0.15% by weight of glycerol monostearate 0.05% by weight ofN,N-bis(2-hydroxyethyl)(C₁₀-C₂₀) alkylamine (® Armostat 300) 0.05% byweight of erucamide.

In top layer C, the PE described above and the PP described above wereadditionally employed in the ratio 40:60. The process parameters(extruder speed) were set in such a way that, in contrast to Example 1,the total thickness of the film was 60 μm, and the thickness of the toplayer on the inside was 3 μm.

EXAMPLE 3

Example 1 was repeated, with the thickness of the film being 70 μm, itsdensity being 0.8 g/cm³, the thickness of the top layer A on the outsidebeing 1.5 μm, the thickness of the top layer C on the inside being 3 μm,and PE and PP being present in the ratio 25:75.

EXAMPLE 4

Example 1 was repeated, with the mixture of the inner top layer Ccomprising, instead of HDPE, 25% by weight of an LDPE (Borealis LE 0609)having a density of 0.923 and a melt flow index of 0.85 g/10 min at 190°C. and 2.16 kg.

COMPARATIVE EXAMPLE 1

Example 1 was repeated, with the thickness of the film being 90 μm. Thetwo top layers had the same composition as the outer top layer A inExample 1, i.e. essentially consisting of random ethylene-propylenecopolymer.

COMPARATIVE EXAMPLE 2

Comparative Example 1 was repeated, but the blow-molding machine wasfitted with a bulge-shaped bottle mold “B” which likewise has avertical, upward-facing lip. However, the geometry of the bottle mold“B” was selected in such a way that a horizontal section at half theheight of the area to be labeled had a length to width ratio of 135 to82 mm with the long side approximately corresponding to a circle havinga radius of 285 mm.

COMPARATIVE EXAMPLE 3

Example 1 was repeated, with the thickness of the film being 40 μm; thethickness of the top layer on the inside was 3 μm.

COMPARATIVE EXAMPLE 4

Example 1 was repeated, with the thickness of the two top layers being0.7 μm.

COMPARATIVE EXAMPLE 5

Example 1 was repeated, with the density of the film being 0.52 g/cm³.

EXAMPLE 5

Comparative Example 3 was repeated, with the density of the film being0.65 g/cm³.

COMPARATIVE EXAMPLE 6

Example 3 was repeated, with the density of the film being 0.86 g/cm 3,and the thickness of the inner top layer being 2 μm.

COMPARATIVE EXAMPLE 7

Example 1 was repeated, with only the outside of the film beingcorona-treated.

COMPARATIVE EXAMPLE 8

Example 1 was repeated, with the thickness of the outer top layer being1 μm.

The raw materials and films were characterized using the followingmeasurement methods:

Melt Flow Index

The melt flow index of the propylene polymers was measured in accordancewith DIN 53 735 at a load of 2.16 kg and at 230° C. and at 190° C. and2.16 kg for polyethylenes.

Melting Points

DSC measurement, maxima of the melting curve, heating rate 20 K/min.

Roughness Measurement

As a measure of the roughness of the insides of the films, the roughnessvalues Rz of the films were measured in accordance with DIN 4768 Part 1and DIN 4777, as well as DIN 4772 and 4774 by means of an S8Pperthometer from Feinprüf Perthen GmbH, Göttingen, by the profilemethod. The measurement head, a single-skid probe system in accordancewith DIN 4772, was fitted with a probe tip having a radius of 5 μm andan cone angle of 90° with a probe force of from 0.8 to 1.12 mN and askid having a radius of 25 mm in the sliding direction. The verticalmeasurement range was set at 62.5 μm, the probe zone to 5.6 mm and thecut-off of the RC filter in accordance with DIN 4768/1 to 0.25 mm.

Density

The density is determined in accordance with DIN 53 479, Method A.

Assessment of the handling properties:

Curl tendency: a film sheet in DIN A4 format is laid with the undersideand the upper side on a flat substrate. After any static charge hasdissipated, whether and to what extent the edges of the film lift upfrom the substrate is assessed and, where appropriate, measured. Thecurl tendency is regarded as good if the edge height is less than 1 mm,moderate if it is up to 2 mm.

Segregation ability: the frequency with which a handling machine takesmore than one film sheet from the stack during loading of a sheet offsetprinting machine or the blow-molding machine is assessed. Thedestackability is regarded as good at an incorrect removal rate of lessthan 1:10,000, poor at greater than 1:5000.

Mold charging: the error rate on laying the label in the blow mold isassessed. Frequent errors are folding, turned-in edges and, in the caseof electrostatic location, incorrect positioning due to movement in themold. The charging ability is regarded as good at an error rate of lessthan 1:10,000, and poor at greater than 1:5000.

Adhesion.

It is assessed (A) whether the edge of the label can be lifted withoutusing a tool, (B) whether a film detached from the substrate at the edgecan be peeled off without destruction, and (C) whether the labeldetaches from the substrate after flexural stressing at a flexuralradius of less than 3 cm. It is regarded as poor if (A) the edgespontaneously detaches in places from more than 1 in 100 blow moldings,if (B) the label detached at the edge can be peeled off withoutdestruction from more than 1 in 100 blow moldings or if (C) the labeldetaches from the substrate after flexural stressing at a flexuralradius of less than 3 cm.

Appearance of the labeled bottle: the number and size of raised bubblesis assessed, and in addition the bubbles are classified by type andsize. The appearance of a labeled bottle is classified as good if lessthan 30 bubbles of the orange-peel type are visible on the label and asmoderate if more than 200 bubbles are visible.

Large bubbles: the appearance of a labeled bottle is classified as goodif not more than 3 bubbles of not greater than 3 mm in diameter and notgreater than 0.5 mm in height are visible. The appearance is regarded aspoor if more than 15 relatively small bubbles of not greater than 3 mmin diameter and not greater than 0.5 mm in height or one bubble ofgreater than 10 mm in diameter or 1 mm in height are evident. Thebottles that count are the worst ones.

The table below shows the properties of the in-mold-labeled, blow-moldedbottles from the examples and comparative examples.

Rough- ness Rz nm Handling Adhesion Appearance Example 1 5.8 good goodgood Example 2 4.7 good good good Example 3 4.6 good good good Example 45.5 good good good Comparative 3.2 good good in the large inflatedExample 1 particles in bubbles contact Comparative 3.0 good good a largenumber of Example 2 small bubbles in individual bottles Comparative 5.3segregation good; good in the individual inflated Example 3 film kinkseasily particles in contact bubbles Comparative 3.1 good poor (detachesat large inflated Example 4 edge flexural test bubbles; gloss poor poor)Comparative 5.5 segregation good; good poor (orange peel) Example 5 filmkinks easily Example 5 5.4 still good good still good Comparative 3.5very good poor (detaches at poor (wavy appear- Example 6 edge, can bede- ance after sponta- tached substantially neous detachment withoutdestruction) from blow molding) Comparative 4.0 moderate good goodExample 7 (segregation flawed) Comparative poor (tendency to good goodExample 8 curl during printing)

1. An in-mold label in a blow-molding process comprising a multilayerdpolypropylene film, said film comprising a base layer an inner top layerfacing a container to be molded and an outer top layer in contact with amold, said inner top layer exhibiting a roughness Rz of at least 3.5 μm.2. An in-mold label according to claim 1, wherein the inner top layercomprises a mixture of at least two polymers which are not compatiblewith one another.
 3. An in-mold label according to claim 2, wherein themixture consists of a polyethylene and polypropylene or polypropylenecopolymer.
 4. An in-mold label according to claim 2, wherein the mixturecomprises PE and PP in a ratio of from 5 to 50% by weight.
 5. An in-moldlabel according to claim 2, wherein the mixture comprises polyethyleneand polypropylene in a weight ratio of polyethylene to polypropylene offrom 1:12 to 5:1.
 6. An in-mold label according to claim 1, wherein thebase layer is an opaque layer that comprises vacuole-initiating fillers,and the density of the film is from 0.65 to 0.85 g/cm³.
 7. An in-moldlabel according to claim 1, wherein the thickness of the film is atleast 50 μm.
 8. An in-mold label according to claim 1, wherein thethickness of the inner top layer is between 0.5 and 5 μm.
 9. An in-moldlabel according to claim 1, wherein the thickness of the outer top layeris between 0.3 and 5 μm.
 10. An in-mold according to claim 1, whereinthe film comprises ethoxylated fatty acid amide in its base layer. 11.An in-mold label according to claim 1, wherein the roughness is inducedby increasing the formation of β-spherolites within said inner toplayer.
 12. A method of using a multilayered polypropylene film as anin-mold label in a blow-molding process in which the label film is laidin the mold of a blow-molding machine and has an inner top layer facinga container to be molded and an outer top layer in contact with a mold,said inner top layer exhibiting a roughness Rz of at least 3.5 μm.
 13. Amethod according to claim 12, wherein the inner top layer comprises amixture of at least two polymers which are not compatible with oneanother.
 14. A method according to claim 13, wherein the mixtureconsists of a polyethylene and polypropylene or polypropylene copolymer.15. A method according to claim 13, wherein the mixture comprises PE andPP in a ratio of from 5 to 50% by weight.
 16. A method to claim 13,wherein the mixture comprises polyethylene and polypropylene in a weightratio of polyethylene to polypropylene of from 1:12 to 5:1.
 17. A methodaccording to claim 12, wherein the base layer is an opaque layer thatcomprises vacuole-initiating fillers, and the density of the film isfrom 0.65 to 0.85 g/cm³.
 18. A method according to claim 12, wherein thethickness of the film is at least 50 μm.
 19. A method according to claim12, wherein the thickness of the inner top layer is between 0.5 and 5μm.
 20. A method according to claim 12, wherein the thickness of theouter top layer is between 0.3 and 5 μm.
 21. A method according to claim13, wherein the film comprises ethoxylated fatty acid amide in its baselayer.